The relation between a NAS server and a port set with a network address given to the NAS server is uniquely decided at 1:1 so that the processing performance of a TCP/IP processor or the NAS server creates a bottleneck to lower the response. A host computer separates: an I/F portion, to which an address which sends a command is given; a NAS server portion; a cache control portion which processes a device; and an I/F portion which accesses an external storage, and accesses them through an internal network 170 so that the corresponding relation between the I/F and the NAS server and the corresponding relation between the address given to the I/F and the NAS server can be arbitrarily reconfigured according to the processing load or the like.